The capsular saccharides of bacteria have been used for many years in vaccines against capsulated bacteria. As saccharides are T-independent antigens, however, they are poorly immunogenic. Conjugation to a carrier can convert T-independent antigens into T-dependent antigens, thereby enhancing memory responses and allowing protective immunity to develop. The most effective saccharide vaccines are therefore based on glycoconjugates, and the prototype conjugate vaccine was against Haemophilus influenzae type b (‘Hib’) [e.g. see chapter 14 of Vaccines (2004) eds. Plotkin & Orenstein. ISBN 0-7216-9688-0].
Another bacterium for which conjugate vaccines have been described is Streptococcus agalactiae, also known as ‘group B streptococcus’, or simply as ‘GBS’. Much of this work has been performed by Dennis Kasper and colleagues, and is described in documents such as references 1 to 9. Conjugate vaccines for each of GBS serotypes Ia, Ib, II, III, and V have been shown to be safe and immunogenic in humans [10&11]. However, there remains a need for further and improved GBS conjugate vaccines.